Dim M2 Finder...

[NateWeatherly]

Advertisement (gone after registration)

I've had an M2 for a year or so and I feel like the viewfinder must be dimmer than normal. I see a lot of people having issues with a dim rangefinder patch, but on my M2 it's so bright that in a lot of situations it drowns out the viewfinder image. I've actually had to tape a little piece of a green gelatin filter over the rangefinder winder to make focusing easier. The frame lines are bright and clear as well. 

 

For reference, the finders in my Contax G2 and my OM1n (with 50mm f/1.8) are both brighter than my M2 finder and a Fuji X-Pro2 is LOADS brighter and clearer.  Compared to both of these my M2 finder has a distinct bluish tint, with the rangefinder patch appearing slightly yellow. 

 

The previous owner had the camera serviced by DAG right before selling it to me (a friend, so I know that he actually did) so maybe this is just how M2 viewfinders are? 

 

From what I've read I don't think that the prism/mirror is documenting. Could it be a matter of the semi-silvered mirror somehow becoming more opaque (oxidized?) over time? Seems like that might make the rangefinder patch extra bright and the finder itself extra dim. 

 

Do you think that replacing the viewfinder window with multi-coated glass would help much? 

 

Thanks!

[TomB_tx]

Doesn’t sound right. My M2 finder is at least as bright as either of my M3s, but my M4 is a bit brighter.

I had DAG put the multi-coated windows in my M6 when he upgraded the “flare fix”, and although he didn’t think the MC windows added much, it is the brightest and clearest of the bunch.

I would suspect the cementing, as I hear the VF image gets dark while the RF patch stays clear, but I haven’t seen that myself.

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[spydrxx]

You definitively have a problem finder as the M2 finder and patch should both be bright. The previous owner may have DAG service the camera body as a normal CLA, but you don't say what, if anything, he did specifically for the dim finder. If it was done recently you might give Don a call, or you could contact Youxin Ye who has "brightened" several finders for me in the past.

[adan]

This link is just for clarity in visualizing the construction and diagnosis (and perhaps, repair) of an M2 viewfinder (or for that matter, any Leica viewfinder M2 through M9 - M3 and M240/later cameras are, or may be, somewhat different):

 

https://www.rangefinderforum.com/forums/showthread.php?t=137673

 

Key points. The "mirror" is just a microscopic (barely atoms thick) coating of metal between two cemented solid blocks of glass, with their "seam" at approximately a 45° angle. Despite being called "silvering," the factory coating is actually vapor-deposited aluminium. The cement in the M2 era was Canada Balsam - more or less that sticky golden sap/resin one finds on the bark of evergreen trees (and often goos-up one's hands - and is also the source of prehistoric Amber), dissolved in solvents. I suspect that Leica switched to a more "modern" chemical cement at some point in the past 60 years, but have no idea what or when, if at all.

 

The usual failure of these viewfinders is separation - a sudden shock breaks the cement bond, and air gets between the two 45° surfaces. In which case the whole viewfinder (except the RF patch) instantly goes entirely black, due to the difference in the indices of refraction of air and the glass.

 

Since the M2 in question is just "darker" and not solid black, it is not separation, but either/both the cement or the aluminium coating may, as mentioned, be oxidizing and darkening.

 

As the link shows, servicing this is NOT a trivial operation. The glass blocks have to be intentionally separated to get at the thin coatings of materials in between, and recoat them (got a vapor-deposition chamber in your basement?). It would not surprise me if DAG noted the darkening, but knew it would not be economically viable to service unless/until a full separation occurred "naturally" and made the camera entirely unusable. Probably costs more than the value of an M2, except via the ad hoc method used by the RFF poster.

Edited May 27, 2018 by adan

[jerzy]

very good explanation, Adan!  I believe that in the time of M2 halfmirror was still silvered while now it is aluminium vapourized. There are some repair shops which do re-mirroring and cementing prisms. I have done as well few experiments with different thickness of halfmirror and best results were with transmission around 20%. Viewer image is a bit darker, RF patch bit more bright, but is is contrasty. 

So, in the case your prism has been replaced it could very well be that the coating was a bit thicker. Prism may be replaced with anotherone with more transmission but as Adan wrote it is not trivial and will cost some money.

[normclarke]

I noted about 4yrs ago that my M4 prism was showing signs of oxidisation. After strip down I had the prism apart and sent it to a local company that aluminised telescope optics, they recoated the prism to the correct density for me for the sum of £25. On return I obtained the proper UV curing adhesive, the rest is history. I sold it later to a leading Leica dealer. Later models of the M4 have the more sound acrylic adhesives and are thus not so prone to fail when dropped!

 

Best,

 

normclarke

Edited May 29, 2018 by normclarke

[NateWeatherly]

Advertisement (gone after registration)

Wow, thanks guys! This is really good info! Really appreciate it!